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Clinical Trial
. 2015 Feb;35(2):213-20.
doi: 10.1038/jcbfm.2014.184. Epub 2014 Nov 12.

Assessing Cerebrovascular Reactivity Abnormality by Comparison to a Reference Atlas

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Free PMC article
Clinical Trial

Assessing Cerebrovascular Reactivity Abnormality by Comparison to a Reference Atlas

Olivia Sobczyk et al. J Cereb Blood Flow Metab. .
Free PMC article

Abstract

Attribution of vascular pathophysiology to reductions in cerebrovascular reactivity (CVR) is confounded by subjective assessment and the normal variation between anatomic regions. This study aimed to develop an objective scoring assessment of abnormality. CVR was measured as the ratio of the blood-oxygen-level-dependent magnetic resonance signal response divided by an increase in CO2, standardized to eliminate variability. A reference normal atlas was generated by coregistering the CVR maps from 46 healthy subjects into a standard space and calculating the mean and standard deviation (s.d.) of CVR for each voxel. Example CVR studies from 10 patients with cerebral vasculopathy were assessed for abnormality, by normalizing each patient's CVR to the same standard space as the atlas, and assigning a z-score to each voxel relative to the mean and s.d. of the corresponding atlas voxel. Z-scores were color coded and superimposed on their anatomic scans to form CVR z-maps. We found the CVR z-maps provided an objective evaluation of abnormality, enhancing our appreciation of the extent and distribution of pathophysiology compared with CVR maps alone. We concluded that CVR z-maps provide an objective, improved form of evaluation for comparisons of voxel-specific CVR between subjects, and across tests sites.

Figures

Figure 1
Figure 1
Axial slices for the normal cohort atlas displaying spatial distributions. (A) Mean CVR values colored according to the scale shown on the right in percentage of BOLD change per mm Hg PETCO2 change. (B) Coefficient of variation values with color scale on right in percentage. BOLD, blood oxygen level-dependent; CVR, cerebrovascular reactivity; PETCO2, end-tidal partial pressure of CO2.
Figure 2
Figure 2
Axial slices displaying the spatial P value results of the Anderson–Darling normality test. All voxels shown were found to have a P value >0.05.
Figure 3
Figure 3
An axial slice from a healthy subject's CVR map is shown on the left displaying the spatial distribution of CVR values colored according to the scale shown on the right in percentage of BOLD change per mm Hg PETCO2 change. The corresponding CVR z-map and its color scale are shown on the right. The CVR z-map provides a perspective on the (statistical) normality of CVR in the CVR map. This figure illustrates the extent of expected high statistical abnormality, as a result of physiologic, technical (both experimental and analytical), and anatomic variation in the subject as well as errors in the matching of voxels during coregistration. BOLD, blood oxygen level-dependent; CVR, cerebrovascular reactivity; PETCO2, end-tidal partial pressure of CO2.
Figure 4
Figure 4
Example set of five patients with varying levels of large vessel cerebral vascular disease chosen from our database and then further analyzed by z-scoring the CVR map relative to a normal atlas. Table 2 provides additional information and commentary for each subject. CVR, cerebrovascular reactivity; ICA, internal carotid artery; L, left; MRA, magnetic resonance angiogram; R, right; VA, vertebral artery.
Figure 5
Figure 5
Example set of four patients with Moyamoya disease and one patient with idiopathic intracranial hypertension, chosen from our database and then further analyzed by z-scoring the CVR map relative to a normal atlas. Table 2 provides additional information and commentary for each subject. CVR, cerebrovascular reactivity; MRA, magnetic resonance angiogram.

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